AGRO 105 Test 2
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What is Soil?
The outer weathered layer of the earth's crust
What is the general soil composition?
- Inorganic particles
- Organic matter
What are the three soil phases?
What is soil texture?
Relative proportions of particles of different sizes
List the three components from largest to smallest.
Sand is roughly how many particles per gram?
6000 particles per gram
What is sand composed of primarily?
What are the characteristics of sand?
- Low surface to volume ratio
- Large volume to pore space ratio
- Low water hold capacity
- Low nutrient holding capacity
- High Percolation Rate
Clay is the smallest of the three textures and has what characteristics?
- (Opposite of sand)
- High surface area to volume ratio
- Small volume to pore space ratio
- High water holding capacity
- High nutrient holding capacity
- Low percolation rate
What are the characteristics of silt?
What is an ideal soil texture?
- 30% sand
- 30% clay
- 30% silt
- 5-10% organic matter (you as a producer will NEVER have 10% )
What is a loam?
A mixture of soil textures
How can a loam be "guestimated"?
- Using the ribbon test:
- Clay - ribbon 3-4 inches
- Sand - ribbon less than 1 inch
What does silt, and intermediate texture always have?
What is soil structure?
The aggregation(clumping) of mineral particles into compound structures
What do larger pore spaces allow for?
Provides aeration and better drainage
What do small pore spaces allow for?
Better water holding capabilities and nutrient holding capabilities
The preferred soil structure consists of?
- 50% pore space - 1/4 air, 1/4 water
- 45% mineral
- 10% organic matter
What are some factors influencing the soil aggregate?
- Soil water content
- freezing and thawing
- plant cover
- farming practice
- soil texture
What is soil aggregate?
The clumping of soil
The best aggregate possesses what?
1/3 sand, 1/3 clay, 1/3 silt
Soil texture and soil aggregate of clay:
- small particle
- small pore to volume ration
- poor aeration
- good water holding
- good nutrient holding
- subject to compaction
Soil texture and aggregate of sand:
- Large particles
- large pore to volume ratio
- good aeration
- poor water holding
- poor nutrient holding
What is bulk density?
weight of soil per unit volume (g/cc)
What are the effects of a high bulk density?
- Reduced air space
- Reduced water storage
- Impedes root growth
- Impedes water production
What are organic factors affecting bulk density?
- Increased organic material decreases bulk density
- Aides in aggregate formation
How does tillage affect bulk density?
- Beneficial effects:
- loosens the soil
- Increases bulk density or compaction
What is the soil profile?
Characterization of the soil by layers to the parent bedrock
What is the top soil?
Typically considered the upper three feet
What are soil horizons?
The defined layers of the top soil
- The organic layer
- typically on surface
- Mineral portion with high OM
- High root concentration
- High microbial concentration
- High leeching of nutrients
- Also considered the subsoil
- Often nutrient rich
- Low aeration due to compaction
- Few Roots
deteriorating plant material
How to remember the order of horizons?
O.A.B.C.R = Oh A Bear Can Run, across horizons ;)
What is the function of water in plants?
- raw material for synthesis of compounds
- solvent for reactions
- medium for solute movement in plant
- source of tugor pressure
What does polar covalent mean?
- Covalent = sharing electrons
- Polar = uneven sharing of electrons
The oxygen in a water molecule..
- greater attraction for shared electrons
- slightly negative
The hydrogen in a water molecule..
- less attraction for shared electrons
- slightly positive
The importance of water being covalent is?
- water phases
- capillary action
- surface tension
- heat capacity
Water is solid at?
0 degrees Celcius
Water is liquid between?
0-100 degrees Celcius
Water is a gas at what temperature?
100 degrees Celcius
What is a universal solvent?
dissolving of one substance in another
What is cohesion?
Attraction between similar compounds (water attracts water)
What is adhesion?
Attraction between dissimilar molecule (water attaches to soil particles)
What is capillary action in reference to water?
The combined action of cohesion and adhesion, why water can stay in soil profile
What are the characteristics of adhesive water?
- attracts dissimilar molecules
- strong bond
- water not available to root
What are the characteristics of cohesion?
- Also known as capillary water
- weakly bonded
- plant roots easily remove water from soil profile
What are the characteristics of gravitational water?
- water held in soil profile against gravity
- temporary, occurs after rain
- very weakly bonded
What are some factors influencing soil/water relations?
- Soil texture - smaller the particle size the greater the surface area which allows more bonding sites for water
- Organic Matter which improves soil structure
What are the characteristics of a saturated soil?
- All pores full, happens after it rains
- generally short termed
- reduces available air content of soil
What is field capacity?
Amount of water held in soil against gravity (50% water, 50% air space)
What is the wilting point?
Water in soil that isnt available to the plant, this includes adhesion
What is the water infiltration rate?
ability of water to penetrate soil profile, also known as percolation rate
What is percolation rate also known as?
water infiltration rate
What is the importance of infiltration rate?
- Getting water to root zone
- Getting excess water out of root zone
- Controlling run-off water
- Controlling soil erosion
Infiltration rate depends on what?
- Soil structure
- Soil texture
- Farming practices
What are the eighteen essential elements required for plant growth and development?
What is the anagram used to remember the eighteen essential elements?
C HOPKNS CaFe Mg
What are the three non-mineral elements?
What are characteristics of minerals?
- available to plant via soil
- dissolve in soil/water solution as ions
- absorbed through plant roots
What are macronutrients?
required in greater amounts by the plant
What are micronutrients?
needed in lesser amounts by plant, but still important
What are the primary macronutrients?
What are the essential micronutrients?
What is the nutrient required in the greatest amount?
What is the function of nitrogen in the plant?
- Stimulates the initiation of new growth
- Is a component of:
- proteins,chlorophyll, nucleic acids, hormones and ATP
What are the available forms of Nitrogen available to the plant?
- Ammonium : NH4+ (converted through bacteria)
What are some symptoms of nitrogen deficiency?
- stunted growth
- lower yields
- lower protein content
What are some symptoms of excessive nitrogen?
- Plant falls over
- delayed maturity
- less drought tolerance
What is the function of phosphorous in the plant?
- energy storage and transfer
- structural support
- encourages lateral root development
What is the function of Potassium in plants?
What two components must fertilizers have?
- Must be made up of salts
- Be soluble in water
What is a cation?
Positively charged ion
What is an anion?
Negatively charged ion
What are polyatomic ions?
two or more elements bonded together to form an ion
What are important polyatomic ions to remember?
What is the purpose of fertilizers?
provide soil nutrients in concentrations required by the specific plant to maximize its productivity
What is the order of the three elements found in fertilizers?
Don't forget to study the fertilizer problems!!!!!!
~~~~~~~~Don't forget to study the fertilizer problems~~~~~~~~~~
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